Fabrication of hollow articles



1963 (1A. ISBELL, JR., ETAL 3,110,090

FABRICATION 0F HOLLLOW ARTICLES Filed May 13, 1960 my f 25 I v 4 l 26- 25 '1 K )f r? /a Wat/V rs.

United States Patent 3,110,090 FABRICATION 0F HOLLOW ARTIQLES Clarence A. lshcll, .Ir., Fergason, Mo and Robert M. Neel, New Douglas, and Theron F. Panls, Aiton, liL, assignors to Olin Mathieson Chemical Corporation,

East Alton, 111., a corporation of Virginia Filed May 13, 1966, Ser. No. 29,063 4 Claims. (Cl. 29-1575) This invention relates to the fabrication of hollow articles and more specifically to the fabrication of hollow articles which are smooth on one side. This application is a continuation-in-part of copending application S.N. 626,722 filed by Clarence A. =Isbell, Jr., Robert M. Neel, and Theron F. Pauls, as co-inventors, on December 6, 1956 and now abandoned.

In the fabrication of hollow sheet metal panels by a well known process two sheets of metal are arranged in stack-like fashion with a design of weld-inhibiting material applied to a portion of one of the adjacent faces of the sheets. The sheets are then welded together in their adjacent areas not separated by the weld-inhibiting material in any suitable manner, as by hot rolling, to form a blank. As the sheets are being welded together by hot rolling they are elongated in the direction of rolling and therefore the design of weld-inhibiting material must be foreshortened in the intended direction of rolling when it is applied to the sheet. After the sheets are welded together to form a blank, they are usually softened as by annealing, and the unjoined portion separated by the weld-inhibiting material is outwardly expanded as by injecting therein a fluid pressure of sufiicient magnitude to permanently distend the sheets in the area adjacent to the weld-inhibiting design, thereby forming a hollow panel. The weld-inhibiting design may assume any desired configuration, for example, a design which will define, after expansion of the blank, a fluid conveying circuit of the type required in refrigerator heat exchanger panels. The aforementioned process is fully described in the patent to Grenell, U.S. 2,690,002 issued September 28, 1954. In accordance with this patent dies may be used in expanding panels fiat on one side, but this is objectionable because of the labor and material required in making the dies and the accompanying increase in cost.

This invention is directed to the fabrication of hollow articles having a smooth side and a distended side, by welding together sheets having different strength characteristics, or differentiable elastic properties and if necessary adequately differentiating the elastic properties prior to expanding the blank. The blank thus formed is clamped between a smooth hard pressure pad and a compressible pressure pad, with the weaker sheet adjacent the compressible pressure pad, and the stronger sheet adjacent the hard pad. The blank is then expanded as by injecting into the unjoined portion a fluid pressure of sufficient magnitude to permanently distend only the weaker sheet to form a hollow panel. To obtain the maximum volume in the hollow portion of the expanded panel the pressure should be such as to permanently distend the weaker sheets between its elastic limit and ultimate rupture strength, but below the elastic limit of the stronger sheet.

As used herein the term smooth refers to a surface devoid of depressions or protrusions in the overall general configuration of the surface. fers to the maximum stress that a material will withstand without permanent deformation.

It is an object of this invention to fabricate an improved hollow panel with one side smooth and the opposite side disten e Another object of this invention is to fabricate an im- The term elastic limit re- 3,1 10,0 9 0 Patented Nov. 12, 1963 proved panel having formed therein a hollow portion, such as fluid carrying conduits, defined by a smooth surface and an opposite surface having protrusions conforming to the hollows.

Another object of this invention is to provide a method of fabricating panels of the general type disclosed in the aforementioned US. Patent No. 2,690,002, in which one of the outer surfaces has a high degree of smoothness.

This invention is directed primarily to the fabrication of metal panels, but in part it is equally applicable to panels fabricated from materials other than metal, such as various plastics, and to panels fabricated fro-m dissimilar materials such as a metal and a plastic joined together with an unjoined portion between the sheets.

Additional objects and advantages will be apparent from the following description and drawings in which:

FIGURES 1-3 illustrate an embodiment of the invention and indicate schematically a process for fabricating a blank from which a hollow smooth sided panel may be formed, and more specifically:

FIGURE 1 is a perspective view of a sheet of metal having applied to a surface thereof a pattern of weldinhibiting material;

FIGURE 2 is a perspective view of the sheet shown in FIGURE 1, with a second metal sheet superimposed thereon in laminar fashion and tacked thereto as by spotwelding, and with the pattern of weld-inhibiting material sandwiched between the sheets;

FIGURE 3 is a perspective view of the sheets of FIG- URE 2 being welded together in a rolling mill to form a blank;

FIGURE 4 is a sectional schematic view of the resultant blank of FIGURE 3 the line 44 in FIGURE 1 indicating the portion of the weld-inhibiting pattern shown in FIGURE 4, and showing the blank positioned in a press, between one embodiment'of a pair of pressure pads; I

FIGURE 5 is a sectional schematic view similar to FIGURE 4 after the pressure pads have been clamped against the blank and the unjoined portion of the blank expanded;

FIGURE 6 is a schematic view of an embodiment of an assembly for controlling the expansion of a blank;

FIGURE 7 is a perspective View of the upper side of the finished panel shown in FIGURE 5; the broken lines indicating areas .-to be trimmed from the ends of the panel;

FIGURE 8 is a perspective view of the reverse side of the panel shown in FIGURE 7 with the areas to be trimmed from the ends of the panel again indicated by broken lines.

Referring to the drawings, FIGURE 1 shows a sheet of metal 1 with a design of weld-inhibiting material 2 applied to a clean surface 3 thereof. The design 2 may be extended to the edge of the sheet as shown at 8 to subsequently form an inlet. The design is foreshortened in the intended direction of subsequent rolling. The surface of the sheet may be cleaned in any conventional manner as by brush-scrubbing.

FIGURE 2 shows a second metal sheet 4 superimposed on the surface 3 of the first sheet 1 to which the weldinhibiting material 2 has been applied. The surface of the second sheet 4- adjacent the first sheet 1 has been previously cleaned in a manner similar to the cleaning of the first sheet. The two sheets are lightly secured together as by spot-welding 5 to prevent relative slippage between the sheets as they are welded together in their adjacent areas not separated by the weld-inhibiting material. After being tacked together the sheets 1 and 4- are usually heated to assure welding together of the sheets as they pass through the mill rolls 6.

FIGURE 3 shows the two sheets 1 and 4 passing between a pair of mill rolls 6 and being welded together to form a blank 7 having an unjoined area defined by the weld-inhibiting material 2. During the rolling opera tion the sheets are elongated in the direction of rolling and reduced in cross-sectional thickness. The initial width of the sheets remains substantially unchanged. The degree of heating, if an and the reduction in thickness of the sheets depends on the inherent characteristics of the metals being welded together and such practice is Well known in the rolling art. Following the initial rolling operation, the blank may be softened as by annealing and cold rolled in keeping with the teaching of the aforementioned patent.

The sheets 1 and 4 are selected so that one of the sheets will have a greater strength than the other sheet. Either sheet may be the Weaker, and sheet 4 will be designated the weaker sheet for purposes of the subsequent description. The sheets may be of the same material but of different thicknesses, and therefore of different strength. When the blank has been fabricated of materials having different inherent strength characteristics, a controlled annealing process may be required in which one of the sheets is fully annealed whereas the other sheet is substantially uneffected by the anneahng treatment. With certain composite copper or aluminum blanks an annealing to soften one of the sheets may be required along with a heat treatment to harden the other sheet. Such methods of sheet differentiating treatments will be more fully discussed hereafter.

For any given pair of sheets the eifect of heat treatment may be determined from an appropriate handbook such as Metals Handbook, 1948 edition, published by The American Society for Metals, Cleveland, Ohio. In addition to copper and aluminum, steel and stainless steel of the same or different characteristics are particularly suitable for the fabrication of smooth sided hollow metal panels. In any event, the resultant blanks have one relatively weaker side which may be permanently distended at a pressure too low to permanently distend the other stronger side.

The following examples set forth the treatment of but a few of the many possible combinations. The examples refer to yield strength rather than elastic limit, however, the elastic limit, which is slightly less than the yield strength, may be determined on the basis of the yield strength for any given metal, by methods well understood in the art.

Example 1 A blank may be fabricated from two sheets of copper alloy, one of the sheets being an electrolytic tough pitch copper containing: 99.90% minimum copper, 0.05% maximum oxygen, 0.003% maximum phosphorus, and 0.03% total or 0.01% each or" other impurities; and the other sheet being a high conductivity bronze containing: 94-96% copper, 0.75l.25% tin, 25% maximum phosphorus, 0.05% maximum lead, 0.01% maximum impurities and the balance zinc. vA pattern of weld-inhibiting material is applied to a surface of one of the sheets and this surface is then welded to a surface of the other sheet in the areas not separated by the weld-inhibiting material by hot rolling at a temperature of 1700 F., and a reduction or 60% in a single pass through a rolling mill. Subsequently, the welded blank may be fully annealed and then cold rolled to an additional reduction of 30% after which it is in the work hardened state having a hardness of 60 Rockwell B and a yield strength of 55,000 p.s.i. for the high conductivity alloy and a hardness of 87 Rockwell B and a yield strength of 67,000 p.s.i. for the electrolytic tough pitch alloy. The blank is then heated at a temperature of 300 C. for 60 minutes fully annealing the electrolytic tough pitch alloy. This temperature is below the annealing temperature of 650 Cffor the high conductivity alloy. The electrolytic tough pitch alloy has then been anneled to a yield strength of about 7,000 p.s.i.

In a blank fabricated from two sheets of aluminum alloy, the first commercially pure aluminum (1100 alloy) and the second 6061 aluminum alloy, a pattern of weldinhibiting material is applied to the clean face of one of the sheets and this face is welded to a clean face of the other sheet in the areas not separated by the weldinhibiting material by hot rolling at a temperature of 950 R, and a reduction of 65% in a single pass through a rolling mill. Subsequently, the welded blank is fully annealed and cold rolled at a reduction of 27%. Except for obtaining a weld and a blank of even thickness, the previous annealing and cold rolling steps have no effect on the mechanical properties of either side of the blank after the following heat treatments. The blank is solution heat treated by holding the entire mass of the blank at a temperature of 970 F. for 10 minutes, followed by an immediate quenching, within five seconds of being removed from the furnace, in water at a temperature of about 50 F. The 1100 alloy is now fully annealed to a 0 temper and the 6061 alloy has now been solution heat treated to the T-4 temper. The blank is next precipitation heat treated to either a temperature of 320 -F. for 16-20 hours or a temperature of 350 F. 'for 6-10 hours which yields the same results. The 1100 alloy now has a yield strength of 5,000 p.s.i. and the 6061 alloy now has a yield strength of 40,000 p.s.i. both at an offset of 0.2%

Referring to FIGURE 4, the resultant blank 7 is positioned between a compressible pressure pad 10 and a hard pressure pad 11. The compressible pressure pad is mounted on a hard backing plate 12 having confining side walls 13 which engage the side wall of the compressible pad limiting outward displacement of the pad. The compressible pressure pad 10 and its backing plate 12 are positioned on a fixed jaw 14 of the press 15 and the hard pressure pad is mounted on the upper jaw 16 secured to a plunger 17 received in a cylinder 18 with a fluid-tight sliding fit. The movable jaw 16 is maintained in a raised position by a spring 19 engaging a shoulder 20 on the I lower end of the cylinder 18 and a shoulder 21 on the plunger 17. The cylinder 18 is fixed with respect to the lower jaw 14 in any appropriate manner as by arms 23. The blank 7 is inserted between the pressure pads with the weaker sheet 4 adjacent the compressible pad 10 and a fluid pressure conveying nozzle 25, attached to a hose 25', is inserted into the inletin the blank. A fluid pressure conveying conduit 24 opens into the upper end of the cylinder 18 for injecting a fluid into the cylinder thereby forcing the plunger 17 downward and the hard pressure pad 11 against the compressible pressure pad 10. A fluid pressure is conveyed through the conduit 24 into the cylinder 13 clamping the hard upper pressure pad 11 against the lower compressible pressure pad 10, the horizontal surfaces of the walls 13 of the backing plate 12 and the stronger sheet 1 of the blank 7.

To assure a smooth-sided hollow article 25 having one side 27 devoid of protrusions, in a pad one inch thick the total compression of a compressible rubber pad 10 should be preferably limited to between twenty and thirty percent for a 30 Shore-Durometer rubber, for a typical blank as previously described. The percentage of compression is controlled by the height of the side walls 13 relative to the thickness of the rubber pad 10. Preferably the compressible pad should also be resilient such as a rubber pad, however, a pad which is not resilient will function properly to a degree but may not be reused.

The outward distention of the unjoined portion 28 of the blank 7 is controlled by the difference between the force exerted within the unjoined pontion of the blank, the resistance of the compressible pressure pad 10, and the strength of the sheet 4. In the embodiment shown in FIGURE 4, this control is obtained by increasing or decreasing the thickness of the compressible pad 1% relative to the height of the backing plate side walls 13.

Referring to FIGURE 4, the process of expanding the blank is as follows: With the valves A, B, C, and D shown in FIGURE 6 closed, valves C and A are opened forcing the hard prmsure pad 11 against the side walls 13 of the backing plate 12, the compressible pressure pad 19, and the stronger side 1 of the blank 7. It is only necessary that suflicient pressure he applied through valve C to firmly maintain the hard pad 11 against the side walls 13. Valve 13 is then opened, exerting the same pressure within the unjoined portion 28 of the blank 7 as is exerted in the hydraulic cylinder 18. Valve C is then closed. The pressure from a pump 3th is then increased sufiiciently to fully expand the weaker plate 4 adjacent the unjoined portion of the blank to form the hollow panel 26. The pressure required will vary depending on the strength of the weaker sheet 4 of the blank and the configuration of the unjoined portion 28, but is above the pressure required to rupture the panel when unrestrained by the pads. Valve A is then closed and valves C and D, are opened, simultaneously releasing the pressure in the cylinder 13 and within the distended portion 31 of the panel. It is usually necessary for these pressures to be released simultaneously. If the pressure within distended portion 31 of the panel 26 is released first the pressure of the compressible pad 10 against the distended portion 31 of the panel may cause the distention to collapse. Conversely, if the pressure within the hydraulic chamber 13 is released first the pressure within the distended portion 51 of the panel 26 will cause the panel to rupture. After the pressures have been released separating the hard and compressible pressure pads the resultant hollow article 26 is removed from the press 15.

As shown in FIGURES and 8 the hollow article 26 is distended on the weaker side 29 and smooth on the opposite side 27 which was against the hard pressure pad 11.

in expanding smooth sided panels by the aforementioned process any excessive distention of the weaker side of the panel may cause the stronger side to be pulled in slightly in the area at which the two walls of the hollow portion of the panel unite. Should this occur, the effect can be eliminated by expanding the weaker side to a lesser degree, or compressing the compressible pad a greater amount. In any event, the stronger side of the panel will not have a permanent outward distention if the force exerted within the unjoined portion of the panel is not of sufi'icient magnitude to distend the stronger side past its elastic limit. Although in the technical sense, some materials will receive a permanent set even when they are stressed within their elastic limit, such a permanent set is very minute and of no practical importance and this invention is intended to include application of the process to such materials.

The same type of procedures may be followed in infiating lanks fabricated of other difierent metals and of metal and plastic adhesively joined together.

Although the invention has been described with particular reference to certain specific embodiments, ma terials, techniques and details, various changes and modifications will be apparent to one skilled in the art and the invention is therefore not to be limited to such embodiments, materials, techniques, or details except as set forth in the appended claims.

We claim:

1. In a process for fabricating a hollow sheet metal panel having a smooth side and an opposite side having distentions formed by the hollow portion of said panel, the steps comprising forming a blank by applying to a portion of a surface of a first weldable ductile metal sheet a design of weld-inhibiting material, positioning adjacent said surface a surface of a second weldable ductile metal sheet having an elastic limit at least finally different from said first sheet, welding said sheets together in the areas of said adjacent surfaces not separated by said weld-inhibiting material, treating said assembly of unified sheets to afiect the elastic limit of at least one of said sheets to more widely differentiate their elastic limits, positioning said assembly between spaced opposing pressure pads, offering differing constraint to said sheets with the pad offering less constraint positioned adjacent the sheet of lower elastic limit and exerting between said sheets in the area separated by said weld-inhibiting material a force of sufficient magnitude to distend one of said sheets beyond its elastic limit but of insufi'icient magnitude to distend the other of said sheets beyond its elastic limit.

2. In a process for fabricating a hollow sheet metal panel having a smooth side and an opposite side having distentions formed by the hollow portion of said panel, the steps comprising forming a blank by applying to a portion of a surface of a first sheet of weldable ductile metal amenable to heat treatment affecting its elastic limit a design of weld-inhibiting material, positioning adjacent said surface a surface of a second sheet of weldable ductile metal having an elastic limit different than said first sheet and also being amenable to heat treatment affecting its elastic limit differently from the effect said treatment has on said first sheet, welding said sheets together in the areas of said adjacent surfaces not separated by said weld-inhibiting material, treating said joined sheets to reduce the elastic limit of the sheet initially having the lower elastic limit and to raise the elastic limit of the sheet initially having the higher elastic limit, positioning said assembly between spaced o posing pressure pads offering differing constraint to said sheets with the pad oifering less constraint positioned adjacent the sheet of lower elastic limit, extering between said sheets in the area separated by said weld-inhibiting material a force of sutlicient magnitude to distend one of said sheets beyond its elastic limit but of insufiicient magnitude to distend the other of said sheets beyond its elatsic limit, whereby upon release of said pressure said panel is permanently distended on one side and substantially smooth on the other side.

3. The process of claim 1 wherein one of said sheets is amenable to an annealing treatment in a temperature range leaving the other unaffected, thereby lowering the elastic limit of the first sheet below that of the other.

4. The process of claim 2 wherein the sheet initially having the lower elastic limit is a work hardened metal and the sheet initially having the higher limit is an age hardenable and work hardened alloy having a solution temperature in the range at which the metal of the other sheet becomes annealed and wherein the treatment is the age hardening treatment of the alloy.

References Cited in the file of this patent FOREIGN PATENTS 

1. IN A PROCESS FOR FABRICATING A HOLLOW SHEET METAL PANEL HAVING A SMOOTH SIDE AND AN OPPOSITE SIDE HAVING DISTENTIONS FORMED BY THE HOLLOW PORTION OF SAID PANEL, THE STEPS COMPRISING FORMING A BLANK BY APPLYING TO A PORTION OF A SURFACE OF A FIRST WELDABLE DUCTILE METAL SHEET A DESIGN OF WELD-INHIBITING MATERIAL, POSITIONING ADJACENT SAID SURFACE A SURFACE OF A SECOND WELDABLE DUCTILE METAL SHEET HAVING AN ELASTIC LIMIT AT LEAST FINALLY DIFFERENT FROM SAID FIRST SHEET, WELDING SAID SHEETS TOGETHER IN THE AREAS OF SAID ADJACENT SURFACES NOT SEPARATED BY SAID WELD-INHIBITING MATERIAL, TREATING SAID ASSEMBLY OF UNIFIED SHEETS TO AFFECT THE ELASTIC LIMIT OF AT LEAST ONE OF SAID SHEETS TO MORE WIDELY DIFFERENTIATE THEIR ELASTIC LIMITS, POSITIONING SAID ASSEMBLY BETWEEN SPACED OPPOSING PRESSURE PADS, OFFERING DIFFERING CONSTRAINT TO SAID SHEETS WITH THE PAD OFFERING LESS CONSTRAINT POSITIONED ADJACENT THE SHEET OF LOWER ELASTIC LIMIT AND EXERTING BETWEEN SAID SHEETS IN THE AREA SEPARATED BY SAID WELD-INHIBITING MATERIAL A FORCE OF SUFFICIENT MAGNITUDE TO DISTEND ONE OF SAID SHEETS BEYOND ITS ELASTIC LIMIT BUT OF INSUFFICIENT MAGNITUDE TO DISTEND THE OTHER OF SAID SHEETS BEYOND ITS ELASTIC LIMIT. 